Power/Performance Bits: Nov. 25

Insect robots on the water; advances in aqueous lithium-ion batteries.


Insect robots on the water

Taking inspiration from water beetles and other swimming insects, academics at the Bristol Robotics Laboratory have developed the “Row-bot,” a robot that thrives in dirty water. The Row-bot mimics the way that one aquatic insect, the water boatman, moves and the way that it feeds on rich organic matter in the dirty water it swims in.

The Row-bot project aims to develop an autonomous swimming robot able to operate indefinitely in remote unstructured locations by scavenging its energy from the environment. When it is hungry, the Row-bot opens its soft robotic mouth and rows forward to fill its microbial fuel cell stomach with nutrient-rich dirty water. It then closes its mouth and slowly digests the nutrients, using the degradation of organic matter to generate electricity. When it has recharged its electrical energy stores the Row-bot rows off to a new location, ready for another gulp of dirty water.

The Row-bot with its mouth open. (Source: Hemma Philamore, University of Bristol/BRL)

The Row-bot with its mouth open. (Source: Hemma Philamore, University of Bristol/BRL)

While the performance of the prototype was inferior to that of the real water boatman, the energy the robot generated from “feeding” still exceeded the energy it required to refuel.

Hemma Philamore, PhD student at Bristol, sees promise for the Row-bot, particularly “in environmental clean-up operations of contaminants, such as oil spills and harmful algal bloom, and in long term autonomous environmental monitoring of hazardous environments, for example those hit by natural and man-made disasters.”

Advances in aqueous lithium-ion batteries

A team of researchers from the University of Maryland and the U.S. Army Research Laboratory have devised a “Water-in-Salt” aqueous lithium-ion battery technology that could provide power, efficiency and longevity comparable to today’s lithium-ion batteries, but without the fire risk, poisonous chemicals, and environmental hazards.

The researchers said their technology holds great promise, particularly in applications that involve large energies at kilowatt or megawatt levels, such as electric vehicles, or grid-storage devices for energy harvest systems, and in applications where battery safety and toxicity are primary concerns, such as safe, non-flammable batteries for airplanes, naval vessels or spaceships, and in medical devices like pacemakers.

“Through this work we were able to increase the electrochemical window of aqueous electrolyte from less than 1.5 Volts to ~ 3.0 Volts and demonstrated high voltage aqueous full Lithium-ion cell with 2.3 Volts, showing for the first time that aqueous batteries could seriously compete in terms of power and energy density with non-aqueous lithium-ion batteries,” said Chunsheng Wang, an associate professor at the University of Maryland.

(Source: University of Maryland)

(Source: University of Maryland)

The team’s key breakthrough was the use of a type of water-based electrolyte containing ultrahigh concentrations of a carefully selected Lithium salt. This approach transformed the battery’s chemistry, resulting in the formation of a thin protective film on the anode electrode for the very first time in a water-based battery.

The high stability of other aqueous batteries has been achieved only at the expense of voltage and energy density and vice versa. However, the formation of an anode/electrolyte interphase in their “Water-in-Salt” electrolyte allowed them to break this inverse relationship between cycling stability and high voltage and to achieve both simultaneously.

According to Kang Xu, a senior research chemist at the Army Research Laboratory, the finding “opens an entirely new avenue to aqueous electrochemical devices, not only batteries, but also devices like supercapacitors and electroplating devices.”

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